The present invention relates to hydrocarbon processing. In particular, the present invention relates to hydrocarbon processor reactor designs which employ onstream catalyst replacement (OCR).
Hydrocarbon processing utilizes catalyst materials to speed up or alter the composition of a product stream. These reactors are costly to operate, especially for the downtime where all the catalysts must be replaced. Catalysts that tend to be used with the heavier-end or more contaminated portion of the crude oil, such as processing of residuum, vacuum gas oil (VGO) feed or materials having high concentrations of catalyst poisons such as nitrogen and sulfur based compounds as well as heavy metals, require more frequent and expensive downtime for catalyst change-out.
A process to handle this on a continuous basis called xe2x80x9cOCRxe2x80x9d is highlighted in U.S. Pat. Nos. 5,589,057; 5,599,440; 5,603,904; 5,076,908; and the like. Each of these preceding patents are completely incorporated herein by reference for all purposes. In general, the OCR process involves a reactor having a cone or screen at the bottom thereof to support the catalyst. The catalyst""s stream enters at the top of the reactor counter-current to the flow of the gas and the hydrocarbon which enters at the bottom. As the feed moves up through the catalyst and contaminants are retained on the catalyst, these particles become heavier and move downward through the reactor towards the entering products stream and are finally withdrawn at the bottom of the reactor. The extracted catalysts can either be reintroduced at the top of the reactor directly, or mixed with fresh catalyst and introduced at the top of the reactor, or reprocessed and injected alone or in combination with fresh catalyst at the top of the reactor, or combinations thereof. This process permits the reactor to run on a longer or continuous basis without downtime for catalyst change-outs. The heavier the feed or the more contaminated the feed, the greater the charge of new catalyst and/or the faster the cycle times downward through the reactor are adjusted to achieve the desired product stream output.
Present OCR design employs passive (non-catalytic) spheres beneath the distributor cone in order to provide for a laterally uniform liquid and gas flow to the moving catalyst bed. The passive spheres thus far used in commercial reactors have been significantly larger than the active catalyst spheres in the OCR. This was thought to help support the cone as well as prevent catalyst loss and screen plugging of the distributor cone at the interface between the catalyst and the product stream introduction. Because of the size, mainly width, of the OCR distributor cone diameters (generally greater than or equal to 4.4 meters) and cone angles of about 60 degrees or greater, the larger packing below the cone causes preferential liquid and gas flow towards the region of least resistance to the flow, namely, the walls of the OCR reactor. This creates poor distribution of the liquid and gas products stream which results in lower product conversion or poor product uniformity. Reactor hot spots are another undesirable result of distribution problems.
Thus, it would be highly desirable to have a reactor capable of achieving more uniform flow across the catalyst bed, i.e., across the diameter of the reactor, especially at the point of the inverted cone.
The invention involves packing the region beneath the distributor cone where the feed and gas enter the reactor with passive spheres having substantially the same diameter as the active catalyst particles above the distributor cone. This ensures a more even distribution of the liquid and the gas through the cone since all the flow paths will have the same resistance. This is achievable even without plugging of the distributor cone screen. However, since the passive packing spheres will be the same size as the catalyst particle, screen designs are utilized in combination with the like-sized passive spheres to ensure that the passive spheres do not clog, i.e., become wedged in the underside of the prior art screen.
Thus, the invention includes a reactor having a distributor cone substantially at one end thereof and including catalyst particles contacting the interior of a distributor cone screen and passive spheres of like size to the catalyst particles contacting the opposite side of the distributor cone, wherein the distributor cone screen separating the catalyst particles from the passive spheres presents openings thereto shaped to preclude the entry of the catalyst or passive spheres within the opening in a plugging orientation. The gas and liquids are withdrawn or optionally recycled after passage through at least a portion if not all of the catalyst material.